FlightCrew is an ePub book file validator. It is available for 64-bit Linux from here, as a .bin "install file".

I never met one of those before, just rpm and deb. How do I install it on a Debian system, preferably via the desktop software tools so it gets hooked into debian's dependency management and all those good things?

"Klinger, do you know how many zoots were killed to make that one suit?" — BJ Hunnicutt, 4077 M*A*S*H

As to whether it needs root permissions to run, you'll have to try it. I'd try as a normal user first, in which case it will either install to your home directory or complain about needing root permissions.

"Insanity: doing the same thing over and over again and expecting different results." (Albert Einstein)